1. Field of the Invention
Aspects of the present invention relate to an outer encoder and an outer encoding method thereof that robustly process a digital broadcasting transport stream, and more particularly, to an outer encoder and an outer encoding method thereof that generate and transmit a dual transport stream including a normal stream and a turbo stream in order to improve the receiving performance of the ATSC (Advanced Television Systems Committee) VSB (Vestigial Side Band) system that is the American-type digital terrestrial broadcasting system, and which encode the turbo stream so as to transmit the turbo stream more robustly.
2. Description of the Related Art
An ATSC (Advanced Television Systems Committee) VSB system, which is an American-type digital terrestrial broadcasting system, is a signal carrier type broadcasting system and uses a field sync signal having a unit of 312 segments. Accordingly, its receiving performance is not good in an inferior channel, and particularly, in a Doppler fading channel.
FIG. 1 is a block diagram illustrating the construction of a transmitter/receiver of an ATSC DTV standard as a general American-type digital terrestrial broadcasting system. The digital broadcast transmitter of FIG. 1 is an enhanced VSB (EVSB) system proposed by Philips that forms and transmits a dual stream provided by adding robust data to normal data of the basic ATSC VSB system.
As illustrated in FIG. 1, the digital broadcast transmitter includes a randomizer 11, which randomizes a dual stream, an RS (Reed-Solomon) encoder 12 in the form of a concatenated coder that adds parity bytes to the transport stream in order to correct errors occurring due to the channel characteristic in a transport process, an interleaver 13, which interleaves the RS-encoded data according to a specified pattern, and a ⅔-rate trellis encoder 14, which maps the interleaved data onto 8-level symbols by performing a ⅔-rate trellis encoding of the interleaved data. The digital broadcast transmitter performs an error correction coding of the dual stream.
The digital broadcast transmitter further includes a multiplexer 15, which inserts a field sync signal and a segment sync signal into the error-correction-coded data as a data format in FIG. 2, and a modulator 16, which inserts a pilot tone into the data symbols into which the segment sync signal and the field sync signal have been inserted by adding specified DC values to the data symbols, performing a VSB modulation of the data symbols by pulse-shaping the data symbols and up-converting the modulated data symbols into an RF channel band signal to transmit the RF channel band signal.
In the digital broadcast transmitter, the normal data and the robust data are multiplexed (not illustrated) according to a dual stream system that transmits the normal data and the robust data through one channel, and the multiplexed data is inputted to the randomizer 11. The input data is randomized through the randomizer 11, outer-encoded through the RS encoder 120, which is an outer encoder, and then distributed through the interleaver 13. Also, the interleaved data is inner-encoded with a unit of 12 symbols through the trellis encoder 14, and then mapped onto the 8-level symbols. After the field sync signal and the segment sync signal are inserted into the coded data, the data is VSB-modulated by inserting a pilot tone into the data, and is converted into an RF signal.
The digital broadcast receiver of FIG. 1 includes a tuner (not illustrated) that converts an RF signal received through a channel into a baseband signal, a demodulator 21, which performs a sync detection and demodulation of the converted baseband signal, an equalizer 22, which compensates for channel distortion of the demodulated signal occurring due to multipath conditions, a Viterbi decoder 23, which corrects errors of the equalized signal and decodes the error-corrected signal to symbol data, a deinterleaver 24, which rearranges the data distributed by the interleaver 13 of the digital broadcast transmitter, an RS decoder 25, which corrects errors, and a derandomizer 26, which derandomizes the data corrected through the RS decoder 25 and outputs an MPEG-2 transport stream.
Accordingly, the digital broadcast receiver of FIG. 1 down-converts the RF signal into the baseband signal, demodulates and equalizes the converted signal, and then channel-decodes the demodulated signal to restore the original signal.
FIG. 2 illustrates a VSB data frame for use in the American type digital broadcasting (8-VSB) system, into which a segment sync signal and a field sync signal are inserted. As shown in FIG. 2, one frame is composed of two fields, and each field is composed of one field sync segment, which is the first segment, and 312 data segments. Also, each segment in the VSB data frame corresponds to one MPEG-2 packet and is composed of a segment sync signal of four symbols and 828 data symbols.
The segment sync signal and the field sync signal illustrated in FIG. 2 are used for synchronization and equalization in the digital broadcast receiver. That is, the field sync signal and the segment sync signal refer to known data between the digital broadcast transmitter and receiver, which known data is used as a reference signal when equalization is performed in the receiver side.
The American type digital terrestrial broadcasting system as illustrated in FIG. 1 is a system that can form and transmit a dual stream that is produced by adding the robust data to the normal data of the existing ATSC VSB system. This system transmits the robust data together with the existing normal data.
However, the American type digital terrestrial broadcasting system of FIG. 1 has the problem that it has almost no effect of improving the inferior receiving performance in a multipath channel in the transmission of the existing normal data, although it transmits the dual stream produced by adding the robust data to the normal data.
That is, it has almost no effect of improving the receiving performance according to an improvement of the normal stream. Also, even with respect to a turbo stream, it does not have a great effect of improving the receiving performance in a multipath environment.
Consequently, it is desirable to process the turbo stream more robustly so as to improve the receiving performance for the turbo stream.